Prognostic Significance of Lymph Node Ratio in Rectal Cancer on Overall Survival: An Alternative not a substitute. A Retrospective Cohort Study

Abstract

Abstract Background: Accurate rectal cancer N staging requires the histopathological evaluation of at least 12 lymph nodes. Retrieval of that count is not always possible, Lymph Node Ratio (LNR) could be used as an alternative. Patients and Methods: Retrospective cohort study on 229 patients who underwent curative surgery for resectable rectal cancer. Receiver Operating Characteristic ROC) curve analysis was used to find the optimal cutoff value for Lymph Node count (LNC), Positive Lymph Nodes count (PLN), and LNR affecting overall survival (OS). The Kaplan-Meier product limit method was used for univariate analysis of factors affecting OS. Log Rank (Mantel-Cox) test was used to test significance. Cox-Regression Hazard model was used to detect the most significant factor affecting OS. Results: ROC curve analysis of PLNs revealed the poor value of the test with a sensitivity 51.9%, at PLNs 4 cutoff value, with shorter mean OS aboveit ( 21.71±11.597 vs. 31.20 ± 16.634 for ≥4 vs. <4). ROC curve analysis of LNC revealed the poor value of the test, with a sensitivity 56% at LNC 12 cutoff value, with longermean Overall Survival (OS) above it ( 28.21±15.432 vs. 22.22±12.97 for LNC ≥12 vs. <12). ROC curve analysis of LNR revealed a good value of the test for predicting survival with a sensitivity 95% at LNR 18.82% cutoff value, with longer mean OS above it (21.44±11.607 vs. 39.82±15.085 for LNR ≥18.8% vs. <18.8%). In Univariate analysis, factors significantly affecting OS were histopathological examination (p = .000), Lymph-Vascular Invasion (LVI) (p =.014), LNC cutoff value (p =.002.), PLN cutoff value (p =.008), LNR cutoff value (p=.000). In Multivariate analysis, the LNR cutoff value of 18.8% was found to be the most significant factor affecting OS (p =.000). Conclusion: Higher LNR with 18.82% cutoff value is an independent adverse prognostic factor affecting OS in resectable rectal cancer. LNR could be considered as a good alternative to absolute number of PLN, particularly in patients with a low LNC. Higher LNC ≥12 was associated with a longer OS; maximum possible lymphadenectomy should be done in every single patient.